The present invention relates to an image sensing apparatus and, more particularly, to an image sensing apparatus which senses an image by using a non-interlace or progressive scanning type image sensing device.
As digital signal processing technique improves, many image sensing apparatuses, such as a video camera, having an image sensing unit and a digital recording and playing unit have been developed.
In those apparatuses, standard video signals are generated by an image sensing unit provided with an image sensing device, such as a CCD, compressed by discrete cosine transform (DCT) and quantization, then the compressed video signals are encoded in a format which is suitable for digital tape recording. Thereafter, the encoded signals are recorded on a tape by a recording head. Upon playing back the tape, errors of reproduced signals read by a real head are corrected, decoded and expanded in an opposite manner to the recording operation, then outputted as reproduced video signals.
An example of an image sensing apparatus is shown in FIG. 27.
In FIG. 27, reference numeral 1001 denotes a lens; 1002, a CCD as an interlace scanning type image sensing device for converting an optical image of an object into electrical signals; 1003, an A/D converter for converting analog signals into digital signals; 1004, a camera signal processing circuit for converting the digitized output of the CCD 1002 into video signals of a unit of field; 1005, a video signal processing circuit for compressing the video signals and transforming the compressed video signals to recording data in a format which is suitable for magnetic recording; 1006, a recording circuit for magnetically recording the recording data on a magnetic tape or the like; 1007, a CCD driver for controlling timing of driving the CCD 1002; 1008, an image memory for storing image data; and 1009, a memory address controller for controlling write/read addresses for writing/reading image data to/from the image memory 1008.
An optical image of the object which passed through the lens 1001 is converted into electrical signals of field, which is composed of odd lines or even lines, by the CCD 1002. The output from the CCD 1002 is converted into digital signals by the A/D converter 1003, then enters the camera signal processing circuit 1004. The camera signal processing circuit 1004 performs aperture correction, high luminance color knee correction, white balance correction, .gamma. correction, matrix operation, addition of a synchronization signal, AF preprocessing, AE preprocessing, and so on. Then, it outputs luminance signals and time division multiplexed color difference signals of two kinds of color difference signals by interlaced field. These luminance signals and time division multiplexed color difference signals enter the video signal processing circuit 1005.
The video signal processing circuit 1005 generates frame image data from image data of two successive fields by using the image memory 1008 controlled by the memory address controller 1009, then divides the frame image data into image data of blocks. Thereafter, the image data of blocks is applied with shuffling process in which image data of blocks is read out in a order that is suitable for progressive coding, orthogonal transform, such as DCT, for transforming the read image data of blocks into orthogonal transform coefficients, quantization for quantizing the orthogonal transform coefficients of block depending upon skew of the orthogonal transform coefficients, such as DCT coefficients, to a low frequency range or to a high frequency range, thereby reducing the amount of data, and coding process for further reducing the amount of data by using Huffman coding, for example.
Further, de-shuffling process for de-shuffling the shuffled and quantized data of blocks is performed by using the image memory 1008 controlled by the memory address controller 1009. Thereby, the luminance signals and the color difference signals are transformed into coded data whose amount is compressed.
Furthermore, the video signal processing circuit 1005 converts the coded data into recording data in a form suitable for magnetic recording, and the recording data is inputted into the recording circuit 1006, then recorded on a magnetic medium.
Most of image sensing devices, such as a CCD, used in a general-use video camera as described above, are composed of a great many number of photoelectric converters (pixels) arranged in two dimensions and a mechanism for sequentially transferring electric charges generated in the photoelectric converters. Upon transferring the electric charges, electric charges generated in the photoelectric converters in every other horizontal line are read out. Therefore, image signals of a half of the pixels in the image sensing device are outputted as image signals of each field in order to improve time division resolution. As for an image sensing device whose surface is covered with a complementary color mosaic filter, electrical charges of pixels in two horizontal adjacent lines are added and read out upon transferring electric charges generated by the photoelectric converters, thereby improving time division resolution as well as sensitivity.
The image signals obtained from the image sensing device as described above are interlaced signals, and a conventional general-use image sensing apparatus applies color conversion, and the like, on the image signals from the image sensing device to generate video signals which agree to television standard, such as NTSC and PAL.
Meanwhile, there is a proposal to output image signals generated by a two dimensional image sensing device as a moving image to a television monitor of television standard, such as NTSC and PAL, as well as output the image signals to an information processing device, such as a computer and a printer, as a still image.
However, image signals which are generated in a conventional manner as described above do not have good vertical resolution since it is sacrificed for improving time division resolution. Therefore, the quality of an image of a field inferiors to the quality of an image inputted by a still image input device, such as a scanner. In a case of printing the image of a field by a video printer or using it as an input image in a computer, since horizontal resolution of the image is much different from vertical resolution of the image, each pixel of the image has a shorter width and a longer length, thereby the obtained image may be blurred and give an unnatural impression. Especially, when the image of a field is directly dealt with by a computer, since the computer deals with each pixel as a square dot, a resulted image will have a rectangular shape having longer sides. Therefore, an image of a field has to be processed, however, the processed image would be of inferior quality.
If an image of an even field and an image of a successive odd field are combined together to make a frame image in order to avoid the aforesaid problem, when an object is moving, the combined frame image would not be a still image of high quality since the object looks differently when sensing an image of the even field and when sensing an image of the odd field. Further, when image signals of a field are obtained by adding electric charges of pixels in two horizontal adjacent lines (pixel addition reading method), vertical resolution is also deteriorated. Accordingly, resolution of a frame image obtained by combining an image of an odd field and an image of a successive even field does not improve. Furthermore, when the combined image is printed by a video printer, the printed image looks unnatural since the resolution in the horizontal direction and that in the vertical direction quite differ from each other, which causes blurring of each pixel in the vertical direction.
In an image sensing apparatus using a conventional image sensing device which read out image signals by adding charges of pixels in two horizontal adjacent lines, as described above, it is difficult to generate video signals of various kinds of television standard and signals for a still image of high quality to be outputted from a still image output medium by using a single image sensing apparatus.
Furthermore, in a case where an image sensing device which reads all of the light receiving pixels by so-called non-interlace or progressive scanning is used, outputted image signals have a format different from that of standard television signals. Accordingly, there is a problem in which the output signals from the image sensing device can not be outputted on an electronic view finder (EVF) or a television monitor.
Further, a general video printer is designed so as not to accept non-standard television signals, therefore image signals outputted from the image sensing device which reads all of the light receiving pixels by non-interlace scanning can not be printed out directly.